This invention relates in general to canned motors. In particular, the invention relates to a pump having a canned motor which has a stator with an internal rotor disposed therein, the stator and the internal rotor being mutually separated fluid-tightly by a can disposed between stator and internal rotor, the stator having stator teeth which extend radially in the direction of the internal rotor and define with appurtenant stator-tooth end faces a receiving space for the internal rotor and the can, and the can lying against the stator-tooth end faces.
A canned motor is a particular embodiment of a wet-rotor motor, in which the winding of the stator is protected against the pumped medium by a cylindrical, maximally thin-walled tube made of high-grade steel or plastic within the air gap between stator and rotor of the motor. The performance range of such motors lies between a few watts up to about 2,000 kW. Canned motors are preferably used in pump units.
EP 0 844 723 A2 shows for example a pump having a generic canned motor. The space within which the stator is disposed and the space within which the rotor is disposed are mutually separated fluid-tightly by a can made of plastic. So that the can may be designed with as small a wall thickness as possible, the can is so dimensioned that it lies against the inner side of the stator and is supported by the stator against internal pressure.
The material thickness of the can cannot be increased arbitrarily in order to design the pump for higher operating pressures, since this would likewise accordingly increase the air gap between rotor and stator and thus cause lower energy density in the working air gap and higher stray field losses. Hence, cans made of plastic involve the problem that at high operating pressures, such as for example in the range of 150 bar to 300 bar and higher, the radial pressure load on the can is so high at points not supported by the stator that the plastic is plastically deformed and tears or is sheared off. As a result, pumped medium penetrates into the region of the stator windings and damages the winding of the stator. The stated pressure load is no problem in comparable wet-rotor pump units having a high-pressure-resistant can made of metal, but the eddy-current and magnetic-field losses in such a can amount to up to several hundred watts, depending on the performance category of the motor.
From DE 10 2012 011 316 A1 there is known a canned motor in which the winding of the stator is executed as a tooth coil winding and T-shaped support elements are provided in the winding grooves, with a vertical part of the support elements mutually insulating adjacent windings within a winding groove and mechanically supporting the support element on the ground of the groove. Similar supported cans are also known from DE 2 101 672 A and JP 2006-067 729 A.
From DE 102 32 389 A1 there is known a canned motor in which a plastic sleeve is supported by the stator such that it may be loaded at high internal pressure hydraulically, and the motor inductance may be changed. With a stator having pole shoes, filler pieces consisting of layers of electrically insulated sheets are disposed between the pole shoes such that they are interconnected so as to form a closed bore which serves as a support for the plastic sleeve.